A routing protocol is a protocol that specifies how routers communicate with each other in order to disseminate information so that the routers may select routes between any two nodes on a network. In many examples, each router has a prior knowledge of the router's immediate neighboring routes, but not of other routes. Routers may share information about the neighboring routes with other routers using a routing protocol so that routers have knowledge of the network topology at large. Examples of routing protocols include Routing Information Protocol (RIP), Open Shortest Path First (OSPF), Interior Gateway Routing Protocol (IGRP), Intermediate System to Intermediate System (IS-IS), Enhanced Interior Gateway Routing Protocol (EIGRP), Intermediate system to intermediate system (Exterior Gateway Protocol (EGP), Border Gateway Protocol (BGP), and Constrained Shortest Path First (CSPF).
A packet is a formatted block of data for transmission over a communications network. A routing protocol packet is a packet formatted in accordance with a routing protocol. Routing protocol packets may be, for example, multicast or broadcast. Consequently, routing protocol packets may add up to a large amount of network traffic on networks with a large number of routers. Furthermore, routers may sometimes be deliberately or inadvertently configured to transmit routing protocol packets with misleading information.
For at least these reasons, Internet Service Providers (ISP) may sometimes use filters to block routing protocol packets. For example, an ISP may block routing protocol packets sent from any subnet not within a determined set of subnets. When a customer of an ISP wants to make devices available on a particular subnet, the customer may ask the ISP to add the particular subnet to the determined set of subnets.